The utility of silanes, especially alkoxysilanes, as masonry water repellents is widely known. Compositions currently in use employ solutions of silanes in various organic solvents such as alcohol, e.g., Seiler U.S. No. 3,772,065, and Brown et al. U.S. Pat. No. 4,342,796, or hydrocarbons, e.g., Linn, U.S. Pat. No. 4,525,213. Principal limitations of such solvent type compositions include the toxicity and the flammability of the solvents employed.
Aqueous silane compositions which are non-toxic and non-flammable have become important as effective masonry water repellent compositions, see, Puhringer, U.S. Pat. No. 4,433,013, Schmidt, U.S. Pat. No. 4,517,375 and DePasquale and Wilson, U.S. Pat. No. 4,648,904. Such compositions can have an important drawback, however, and that is that the pH may tend to drift and then the silane reacts with water and polymerizes. This reduces efficacy by reducing the content of active, water-repellent ingredient. Moreover, the pH of the system may shift when additives are included such as a biocide, which is commonly added to retard growth of fungi and the like. Although the stability of the water-containing emulsions can be enhanced to some extent by refrigerating them, or the problem of reduced efficacy can be avoided by using the emulsions soon after preparation, both expedients are not cost-effective and may in some cases cause waterproofing contractors to go back to the above-mentioned solvent borne, non-aqueous compositions.
Although the prior art has frequently demonstrated that silanes dispersed in water react to form silicone resins, see, e.g., Hatcher et al., U.S. Pat. No. 2,683,674 and Raleigh, U.S. Pat. No. 4,175,159, no easy way has been suggested to stabilize them. In some cases, the pH of the system has been adjusted to increase the rate of resin formation, e.g., Deubzer et al., U.S. Pat. No. 4,552,910 and Ona et al., U.S. Pat. No. 4,228,054, but pH control was not suggested as a stabilizing means. Stable hydrolyzed silane impregnating solutions useful as water repellents can also be prepared by dissolving some silanes in water as reported in the above-mentioned Puhringer and Schmidt patents, but they deliberately hydrolyze the silanes and do not produce a stable hydrolyzed silane composition. Wilson, in commonly assigned U.S. Patent Application, Ser. No. 189,146, filed May 2, 1989, now allowed, discloses that hydrolytically stable, water-based, normally hydrolyzable silane emulsions may be prepared by selecting appropriate silanes (largely water insoluble) and appropriate emulsifiers, if the pH is maintained in a predetermined pH stable range, typically 6-8, with a buffering compound. Additionally, Wilson, in commonly assigned U.S. Patent Application, Ser. No. 317,714, filed Mar. 1, 1989, now allowed, discloses buffered silane emulsions compositions in combination with expanded perlite.
However, modern environmental concerns of air quality have made it desirable to develop water-repellents for porous substrates having low levels of volatile organic compounds when cured. Compounds of this nature are especially desirable in light of the increasingly stringent standards on volatile organics set forth by the Environmental Protection Agency (EPA). To this end, it has now been discovered that the buffered silane emulsions of the present invention are eminently suitable for both providing stable compositions useful in rendering masonry, cement and expanded perlite surfaces water repellent, and possessing a sufficiently low volatile organic compound content when cured to satisfy even the most stringent air quality standards.
When used herein and in the appended claims the term "compound for buffering the pH of said composition within said determinable pH stable range" contemplates any substances or combination of substances, which, when dissolved in water produce a solution which resists a change in its hydrogen ion concentration upon the addition of acid or alkali. Although this will call to the mind of those skilled in this art a large family of buffering compounds, numerous illustrations of typical buffering compounds will be set forth hereinafter and in the working examples.